fix: save an edited HTML event description as plain text and keep notes in its format

components/calendar/__tests__/event-description-html.test.tsx

@@ -1,4 +1,4 @@
-import { render, screen, fireEvent } from '@testing-library/react';
+import { render, screen, fireEvent, waitFor } from '@testing-library/react';
 import { describe, it, expect, vi } from 'vitest';
 import { EventDetailPopover } from '../event-detail-popover';
 import { EventModal } from '../event-modal';
@@ -68,3 +68,38 @@ describe('HTML event descriptions', () => {
     expect(container.querySelector('.pr-text')?.textContent).toBe('a <b> c');
   });
 });
+
+describe('saving an HTML event description from the editor', () => {
+  async function save(event: CalendarEvent, newDescription?: string): Promise<Partial<CalendarEvent>> {
+    const onSave = vi.fn().mockResolvedValue(undefined);
+    render(<EventModal event={event} calendars={[calendar]} onSave={onSave} onClose={vi.fn()} currentUserEmails={['me@example.com']} />);
+    fireEvent.click(screen.getByText('events.edit'));
+    if (newDescription !== undefined) {
+      fireEvent.change(screen.getByPlaceholderText('form.description'), { target: { value: newDescription } });
+    }
+    fireEvent.click(screen.getByText('form.save'));
+    await waitFor(() => expect(onSave).toHaveBeenCalledTimes(1));
+    return onSave.mock.calls[0][0] as Partial<CalendarEvent>;
+  }
+
+  // Other clients would read the text as HTML and run its lines together.
+  it('labels an edited description as plain text', async () => {
+    const data = await save(htmlEvent(), `${TEXT}\nMore`);
+    expect(data.description).toBe(`${TEXT}\nMore`);
+    expect(data.descriptionContentType).toBe('text/plain');
+  });
+
+  it('leaves an untouched HTML description as it was', async () => {
+    const data = await save(htmlEvent());
+    expect(data).not.toHaveProperty('description');
+    expect(data).not.toHaveProperty('descriptionContentType');
+  });
+
+  // Stalwart writes a set type as STYLED-DESCRIPTION, which many clients skip.
+  it('sends no type for an event that had none', async () => {
+    const event = { ...htmlEvent(), description: 'old', descriptionContentType: undefined } as unknown as CalendarEvent;
+    const data = await save(event, 'new');
+    expect(data.description).toBe('new');
+    expect(data).not.toHaveProperty('descriptionContentType');
+  });
+});

components/calendar/calendar-app.tsx

@@ -60,6 +60,7 @@ import { useIsFocusedProTab, useIsPaneScoped } from "@/hooks/use-pane-context";
 import { useProMultiAccountCalendars } from "@/hooks/use-pro-multi-account-calendars";
 import { ResizeHandle } from "@/components/layout/resize-handle";
 import { buildDuplicateEventData } from "@/lib/calendar-duplicate";
+import { descriptionWithNote } from "@/lib/calendar-description";
 import { filterTasksByCalendars } from "@/lib/calendar-tasks";
 import { baseEventStoreId, isServerRecurrenceInstance } from "@/lib/recurrence-instances";
 import { deleteOccurrence, saveOccurrenceEdit, type EventEditorState } from "@/lib/recurrence-scope-edit";
@@ -1532,13 +1533,10 @@ export function CalendarApp({ linkSegments: routeSegments }: CalendarAppProps =
   const handleSaveNoteFromDetail = useCallback(async (note: string) => {
     if (!detailEvent || !client) return;
     const timestamp = format(displayNow(), "yyyy-MM-dd HH:mm");
-    const separator = `\n\n--- ${timestamp} ---\n`;
-    const newDescription = detailEvent.description
-      ? `${detailEvent.description}${separator}${note}`
-      : `--- ${timestamp} ---\n${note}`;
+    const fields = descriptionWithNote(detailEvent, `--- ${timestamp} ---`, note);
     try {
-      if (!(await updateEvent(client, detailEvent.id, { description: newDescription }))) return;
-      setDetailEvent({ ...detailEvent, description: newDescription });
+      if (!(await updateEvent(client, detailEvent.id, fields))) return;
+      setDetailEvent({ ...detailEvent, ...fields });
       toast.success(t("detail.note_saved"));
     } catch (error) {
       toast.error(describeError(error, t("notifications.event_error")));

components/calendar/event-modal.tsx

@@ -9,7 +9,7 @@ import { LinkifiedText } from "@/components/ui/linkified-text";
 import { X, Trash2, Users, CalendarDays, CopyPlus, Pencil, Clock, MapPin, Video, Repeat, Bell, AlignLeft, AlertTriangle, MoreVertical } from "@/components/icons";
 import { IconButton } from "@/components/ui/icon-button";
 import { findMeetingLink, locationAction, mapsUrl, primaryLocationName } from "@/lib/event-links";
-import { descriptionAsText } from "@/lib/calendar-description";
+import { descriptionAsText, isHtmlDescription, plainDescriptionFields } from "@/lib/calendar-description";
 import { ParticipantStatusBadge } from "./rsvp-buttons";
 import { format, parseISO, addHours, isSameDay } from "date-fns";
 import type { CalendarEvent, Calendar, CalendarParticipant, CalendarEventAlert, CalendarRecurrenceRule } from "@/lib/jmap/types";
@@ -791,8 +791,11 @@ export function EventModal({
     // On an existing event the empty string is how a description gets cleared, but
     // sending it on creation writes a `DESCRIPTION:` with nothing after it — which
     // invitation e-mails then render as a "Description" heading over blank space.
-    if (trimmedDescription || event) {
-      data.description = trimmedDescription;
+    // An HTML description the user did not touch stays as it was; one they
+    // edited is saved as the plain text it now is.
+    const keepsHtml = !!event && isHtmlDescription(event) && trimmedDescription === eventDescription.trim();
+    if ((trimmedDescription || event) && !keepsHtml) {
+      Object.assign(data, plainDescriptionFields(event, trimmedDescription));
     }
 
     if (!event) {
@@ -941,7 +944,7 @@ export function EventModal({
       savingRef.current = false;
       setIsSaving(false);
     }
-  }, [title, description, location, virtualLocation, startDate, startTime, endDate, endTime, allDay, calendarId, calendars, recurrence, customRule, useDefaultAlerts, defaultAlerts, alertRows, preservedAlerts, attendees, initialAttendees, sendInvitations, currentUserEmails, userIsOrganizer, resolveContactName, event, onSave, isSaving, t]);
+  }, [title, description, location, virtualLocation, startDate, startTime, endDate, endTime, allDay, calendarId, calendars, recurrence, customRule, useDefaultAlerts, defaultAlerts, alertRows, preservedAlerts, attendees, initialAttendees, sendInvitations, currentUserEmails, userIsOrganizer, resolveContactName, event, eventDescription, onSave, isSaving, t]);
 
   // The user's own answer, and the owner's in a calendar shared with them
   // (lib/calendar-delegate.ts).

lib/__tests__/calendar-description.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from 'vitest';
+import { descriptionWithNote } from '@/lib/calendar-description';
+
+// The quick note in the event popover is added to the description.
+
+describe('descriptionWithNote', () => {
+  it('adds a note to an HTML description as an HTML paragraph', () => {
+    const fields = descriptionWithNote(
+      { description: '<p><b>Agenda</b></p>', descriptionContentType: 'text/html' },
+      '--- 2026-11-02 10:00 ---',
+      'Call <Bob> & Ann\nabout it',
+    );
+    expect(fields).toEqual({
+      description: '<p><b>Agenda</b></p><p>--- 2026-11-02 10:00 ---<br>Call &lt;Bob&gt; &amp; Ann<br>about it</p>',
+    });
+  });
+
+  it('adds a note to a plain description as text', () => {
+    expect(descriptionWithNote({ description: 'Agenda', descriptionContentType: 'text/plain' }, '--- t ---', 'Call Bob'))
+      .toEqual({ description: 'Agenda\n\n--- t ---\nCall Bob' });
+    expect(descriptionWithNote({ description: '' }, '--- t ---', 'Call Bob'))
+      .toEqual({ description: '--- t ---\nCall Bob' });
+  });
+});

lib/__tests__/plugin-host-calendar-tasks.test.ts

@@ -204,6 +204,16 @@ describe('api.calendar', () => {
     await expect(call(WRITE, 'calendar.updateEvent', 'e1', {})).rejects.toThrow(/patch is empty/);
   });
 
+  // A plugin writes plain text; left labelled text/html, other clients would
+  // run its lines together.
+  it('labels a description written over an HTML one as plain text', async () => {
+    client.getCalendarEvent.mockResolvedValue(event({ description: '<p>Old</p>', descriptionContentType: 'text/html' }));
+    await call(WRITE, 'calendar.updateEvent', 'e1', { description: 'New\nlines' });
+    expect(client.updateCalendarEvent).toHaveBeenCalledWith('e1', expect.objectContaining({
+      description: 'New\nlines', descriptionContentType: 'text/plain',
+    }), false, undefined);
+  });
+
   it('includes the virtual birthday calendar in listCalendars only when contacts:read is held and showBirthdayCalendar is enabled', async () => {
     useSettingsStore.setState({ showBirthdayCalendar: true, birthdayCalendarColor: '#f59e0b' });
     // Plugin without contacts:read does not see the birthday calendar

lib/calendar-description.ts

@@ -1,4 +1,5 @@
 import { htmlToPlainText } from '@/lib/html-to-text';
+import { escapeHtml } from '@/lib/email-sanitization';
 
 interface DescribedEvent {
   description?: string | null;
@@ -20,3 +21,38 @@ export function descriptionAsText(event: DescribedEvent): string {
   if (!description || !isHtmlDescription(event)) return description;
   return htmlToPlainText(description, { paragraphSpacing: true });
 }
+
+/**
+ * The fields that write `text` as the description of `event`. An event whose
+ * description had another type (text/html) is relabelled text/plain, or other
+ * clients would read the text as HTML and run its lines together. Events
+ * without a type keep none: Stalwart writes a set type to ICS as
+ * STYLED-DESCRIPTION, which many CalDAV clients do not read.
+ */
+export function plainDescriptionFields(
+  event: DescribedEvent | null | undefined,
+  text: string,
+): { description: string; descriptionContentType?: string } {
+  const type = event?.descriptionContentType?.trim();
+  if (type && !/^text\/plain\b/i.test(type)) return { description: text, descriptionContentType: 'text/plain' };
+  return { description: text };
+}
+
+/**
+ * The description of `event` with a note added under `heading`. An HTML
+ * description gets the note as an HTML paragraph, so it keeps its own
+ * formatting and stays text/html.
+ */
+export function descriptionWithNote(
+  event: DescribedEvent,
+  heading: string,
+  note: string,
+): { description: string; descriptionContentType?: string } {
+  const description = event.description ?? '';
+  if (description && isHtmlDescription(event)) {
+    const lines = [heading, ...note.split(/\r?\n/)].map(escapeHtml).join('<br>');
+    return { description: `${description}<p>${lines}</p>` };
+  }
+  const text = description ? `${description}\n\n${heading}\n${note}` : `${heading}\n${note}`;
+  return plainDescriptionFields(event, text);
+}

lib/plugin-sandbox/host-api-calendar.ts

@@ -34,6 +34,7 @@ import { expandRecurringEvents } from '../recurrence-expansion';
 import { buildParticipantMap } from '../calendar-participants';
 import { parseDurationSeconds } from '../calendar-event-normalization';
 import { parseAlertOffset, withOwnAlertIds } from '../calendar-alerts';
+import { plainDescriptionFields } from '../calendar-description';
 import { patchPath } from '../jmap/patch-object';
 import { isValidEmail } from '../validation';
 import { getEffectiveTimeZone } from '../timezone';
@@ -537,6 +538,8 @@ export async function doCalendarUpdateEvent(id: unknown, patch: unknown): Promis
     updates.calendarIds = { [await pickCalendar(client, method, data.calendarId, false)]: true };
   }
   const existing = await eventForMutation(client, method, eventId);
+  // A plugin writes plain text, also over an HTML description.
+  if (updates.description !== undefined) Object.assign(updates, plainDescriptionFields(existing, updates.description));
 
   const timeKeys = ['start', 'end', 'duration', 'timeZone', 'isAllDay'] as const;
   if (timeKeys.some((k) => data[k] !== undefined)) {